Generally, in fabrication of an IC device, a photolithography (or lithography) process may be utilized to print/pattern various layers of a circuit design onto a surface of a silicon (Si) substrate for creating various devices (e.g., transistors) and circuits to form the IC device. In lithography, typically a ultra-violet (UV) light/beam is radiated onto a photomask, which may mask or expose areas on the substrate that are to be blocked from or patterned by the UV light, respectively. With continued progress of the semiconductor industry toward shrinking technology nodes and a high-volume manufacturing model, a need exists to shrink the wavelength used for photolithography in order to print higher resolution features. One such wavelength to achieve this scaling is in the extreme UV (EUV) region of the electromagnetic spectrum; hence a need exists for a compatible EUV source of sufficient power and subsequent distribution system. However, development and implementation of such systems have been slow. Although a single-source high-power free-electron laser (FEL) system, which is widely deployed around the world at scientific user facilities, may be utilized to provide EUV light, challenges such as compatibility of a FEL system with a fabrication facility (fab), total output power, economic considerations, and the like remain. Additionally, distribution of EUV light from a single high-power source to multiple scanners (e.g., associated with multiple photomasks) without a significant loss (e.g., absorption of EUV light by elements in the system) is inherently challenging.
FIG. 1A illustrates example components of a FEL and a beam distribution network. A FEL is divided into several key components, namely the linear accelerator (Linac) and radiator/end station. The Linac is composed of an electron (e) source, a gun/injector 101, and a series of electron accelerators 103, which are typical superconducting radio frequency (SRF) cavities. The electron gun/injector defines the parameters of the generated electrons, while the SRF cavities accelerate the electrons to relativistic speeds. For an FEL, undulators 105 are used to oscillate the electrons thereby generating radiation proportional to the undulator period and magnetic strength for a given electron beam energy. After the undulators 105, the electron beam is either dumped at 107 or recycled and the generated radiation is utilized at the designated end station. In lithography, a beam distribution network 109 may be utilized to distribute EUV sub-beams 111 to EUV scanners 113.
FIGS. 1B through 1D illustrate example light distribution networks associated with a photolithography process. FIG. 1B illustrates an undulator switchyard network that may be utilized to split an FEL beam. By passing the beam through a plurality of undulators 115, consisting of a series of alternating polarity magnets, and electron beam switches 117, which are selectable polarity magnets used to direct the electron beam to each undulator, the beam may oscillate according to the magnetic field direction of each undulator and can produce multiple isolated EUV photon beams 119 for distribution to multiple scanners. However, issues associated with an undulator switchyard network include a high cost and a complex design for manipulating the electron beam through the undulators. FIG. 1C illustrates a time-multiplexing network where a series of mirrors 121 may be utilized to reflect a single EUV beam 123 onto a series of scanners 125 one at a time. However, as the EUV beam may be reflected only to one scanner at a time, this method could not support the simultaneous use of multiple scanners in a high volume manufacturing process. FIG. 1D illustrates a split edge mirrors network where a focused EUV beam 127 may be reflected onto a mirror 129 that is at a grazing incidence angle (less than 30 degrees relative to the surface), wherein an edge of the mirror may reflect a portion of the EUV beam to a scanner corresponding to that mirror. In this network, a plurality of mirrors may be utilized to provide simultaneous EUV beams to corresponding scanners. However, there could be substantial loss in power of the reflected EUV beams where the loss may be due to manufacturing and polishing techniques in the optical industry, high surface roughness and non-uniformity at the edges of the mirrors, or the like issues that could reduce reflectivity of the EUV beams at the edges of the mirrors.
A need therefore exists for a methodology for splitting a high-power FEL beam and, without substantial power loss, providing simultaneous EUV beams to photolithography scanners.